The invention relates generally to the field of heart simulators, and in particular to a simulator providing temporally dependent waveforms simulating implanted hemodynamic sensor signals.
Cardiac resynchronization therapy (CRT) is an established therapy for patients with congestive systolic heart failure and intraventricular electrical or mechanical conduction delays. CRT is based on synchronized pacing of the two ventricles according to the sensed natural atrium signal that determines the heart rhythm. The resynchronization task demands exact timing of the heart chambers so that the overall stroke volume is maximized for any given heart rate (HR). Optimal timing of activation of the two ventricles is one of the key factors in determining cardiac output. The two major timing parameters which are programmable in a CRT device and determine the pacing intervals are the atrioventricular (AV) delay and interventricular (VV) interval. The AV delay is defined herein as the delay from an atrial event that triggers filling of the atrium to a ventricular event that triggers blood ejection from the ventricle. The VV interval is defined herein as the interval between the pacing signal for the left ventricle to the pacing signal for the right ventricle.
Rate responsive pacemakers were designed in the 1980's and 1990's that allow the atrial pacing rate to automatically change according to combined inputs from two implanted sensors typically, accelerometer and minute ventilation sensors. The rate responsive system give a more physiologic pacing to Bradycardia patients and allow higher cardiac output at exercise conditions.
Zachary I. Whinnett et al in “Haemodynamic effects of changes in AV and VV delay in cardiac Resynchronization Therapy show a consistent pattern: analysis of shape, magnitude and relative importance of AV and VV delay”, Heart published online, 18 May 2006, doi:10.1136/hrt.2005.080721, studied the importance of the AV delay and VV interval optimization in CHF patients. The authors conclude that changing the AV and VV delay result in a curvilinear and reproducible acute blood pressure response. This shape fits very closely to a parabola which may be helpful in designing a streamlined clinical protocol to select optimal AV and VV delay.
Various types of implantable electrodes are currently available which generate intra-cardiac electrograms (IEGMs). These electrodes are bi-directional and are capable of both outputting electrical signals reflecting heart electrical activity and receiving electrical impulses to affect heart activity. Various types of hemodynamic sensors are also available reflecting heart mechanical behavior, including without limitation, impedance sensors, pressure sensors and cardiac wall accelerometers, QT interval sensors and non-invasive hemodynamic sensors. However, there are currently no commercially available CRT devices that modify the AV delay and VV interval responsive to the implanted hemodynamic sensors in an adaptive, closed loop system. The ability to design and validate such system is a major technological hurdle for developing and bringing to market closed loop physiological pacemakers and defibrillators that will deliver optimal therapy to CHF and other heart disease patients. In particular the design and validation of the control system which processes the data and makes the appropriate adaptation and classification of patient condition on-line would be greatly enhanced by an appropriate simulator.
Cardiac Output (CO) is defined as the blood volume in milliliters pumped by the heart in one minute. HR and stroke volume, defined as milliliters of blood pumped/systole, determine CO. CO is influenced by the autonomic nervous system in that 1) sympathetic stimulation increases heart rate and stroke volume and 2) parasympathetic stimulation slows heart rate. CO is also influenced by increased venous return, as would occur during exercise. The increased venous return causes greater stretch of the cardiac fibers resulting in greater contraction (i.e., increased stroke volume). This increase in stroke volume due to increased venous return is called Frank-Starling law of the heart.
Contractility of the heart is a major determinant of its ability to pump blood around the body, which is required for the functions of all organs. Because the heart is a muscle, it can adapt to different conditions/requirements that directly affect its contractility and efficiency.
U.S. Pat. No. 3,833,865 to Palmer, issued Sep. 3, 1974, the entire contents of which is incorporated herein by reference, is addressed to a heart simulator which generates an electric waveform similar to that produced by the human heart. Unfortunately such a device is neither responsive to the output of an adaptive CRT device, nor is their any provision for hemodynamic sensor simulation.
U.S. Provisional patent application Ser. No. 60/656,392 filed Feb. 28, 2005 to Rom, entitled “Adaptive Cardiac Resynchronization Therapy and Vagal Stimulation System”, the entire contents of which is incorporated herein by reference, is addressed to a method an apparatus for optimizing cardiac resynchronization therapy devices and vagal stimulators.
U.S. Provisional patent application Ser. No. 60/685,464 filed May 27, 2005 to Rom, entitled “Ventricle Pacing During Atrial Fibrillation Episodes”, the entire contents of which is incorporated herein by reference, is addressed to a system that learns to associate ventricle-atrial intervals with temporal patterns of at least one hemodynamic sensor using neural network processing.
U.S. Provisional patent application Ser. No. 60/897,513 to Rom, entitled “Intelligent Control System for Adaptive Cardiac Resynchronization Therapy Devices” filed Jul. 17, 2006 to Rom, the entire contents of which is incorporated herein by reference, is addressed to an adaptive CRT control system that achieves optimal AV delay and VV pacing intervals with temporal patterns of stroke volume comprising a learning module and an algorithmic controller module supervising the learning module.
International patent application S/N PCT/IL2004/000659 published Jan. 25, 2005 as WO 2005/007075 to Rom, entitled “Adaptive Resynchronization Therapy System”, and filed as U.S. patent application Ser. No. 10/565,279 Jan. 20, 2006, the entire contents of each of which is incorporated herein by reference, is addressed to a system including a learning module and an algorithmic module for learning a physiological aspect of a patient body and regulating the delivery of a physiological agent to the body. Such an adaptive system is advantageous however its development and validation would be simplified by the existence of a heart simulator providing signals simulating hemodynamic sensors.
Thus there is a need for a heart simulator that generates simulated IEGMs and simulated hemodynamic sensor outputs. Preferably the simulated outputs would be responsive to an adaptive CRT device. Such a heart simulator would be particularly useful for the development of closed loop pacemaker and defibrillator controllers working according to implanted hemodynamic sensors thereby shortening the lead time before in-vivo pre-clinical and clinical experiments can begin.